I don't know why you are quoting spamhaus definition for spam, that is not relevant for the GP. Neither is the can-spam acts definition.

I use (and suspect the GP does too) use something like the following definition:Spam is email you don't want - it doesn't matter if you signed up with a company or not if you don't want a particular email it is spam.

Now as a practical matter I tend to click unsubscribe if it exists, mostly because otherwise the spam filters quality drops too far, but I still consider it spam.